I encounter one problem that I can't solve : Using TCS, I am trying to get
an injector able to parse a file which may contain optional tokens with a
default value. More over, these token have their values in only three
predefined ones.

So, I thought to use km3 enums in my metamodel :
How to handle enums used in KM3 in TCS ?

When the token do not appear in the text, how can I recognize it anyway as
defining the default value in the model ?